The conventional use is for dispensing in small doses, e.g. a few ml. The containers and pumps are usually of plastics material. The pump is a module with a dip tube, and is screwed onto the container outlet neck. The discharge nozzle is usually integral with the top of the plunger, with the outlet passage and valve provided through the plunger above an inlet valve, at the bottom of the pump body.
This construction has proved simple and reliable. However, it does have some problems.
Firstly, the movement of the nozzle during dispensing can be a nuisance if accurate dispensing is wanted.
Secondly, there are problems in locking of the plunger for transport. The plunger may be locked in the "up" position, by a tall collar which fits around it to prevent depression. See e.g. U.S. Pat. No. 4,479,589. The projecting plunger takes up a lot of space. If the plunger is locked in the "down" position, e.g. by a screw engagement of the plunger head with an opening in the pump body, this is more compact. However, the locking action requires the head to be depressed and turned at the same time, causing an undesirable dribble from the swinging nozzle.